Patent GB-877047-A (GB)
Title: Contact printing apparatus
IPC: G03B27/20
Filed: 1960-05-17
Abstract: 877,047. Contact printing apparatus. DITTO Inc. May 17, 1960 [May 22, 1959], No. 17367/60. Class 98(2) An apparatus for contact printing has an exposure frame of the vacuum type, a radiant energy source (e.g. a lamp) movable between two terminal positions, means actuated by the moving energy source to deenergize the source and release the vacuum in the frame, and means actuated when the vacuum reaches a predetermined degree to set the energy source in motion. The vacuum frame comprises a rectangular framework 40, within which is secured under tension a resilient blanket 42; the blanket has a continuous lip 45 extending round all four sides, which lip forms a vacuum seal with an underlying glass plate 31. The original, transfer, and copying sheets are laid on the plate 31, a porous cushion 160 being interposed between these sheets and the blanket 42. In the apparatus shown, the photographic copy is made by heat radiation, the source being a heat lamp 60. This is mounted on a carriage 62 supported on wheeled trucks 67, 68 which can run along rails 63, 64; thus the lamp can traverse the whole under-side of the glass plate 31 to effect the exposure, from a terminal position at one end to a terminal position at the other end. The movement is effected by a screw 71 driven from a motor 34, as the drive screw rotates, a nut 73 mounted thereon and engaging with the lamp carriage 62 moves the latter along the length of the screw. At each end of the traverse are limit switches 80, 81. Actuation of either switch de-energizes both lamp 60 and motor 34, thus terminating the exposure period. The vacuum frame hinges at one end on a pin 37, and is lifted open by a handle 59. Evacuation of the space 38 under the blanket takes place through a nipple 46 on the latter. This is connected, by tubes 52, 53, 49, with a coupling member 48. When the frame is closed, this enters into a socket 55 connected by a line 37 to a vacuum pump 32, at the same time closing a cover switch which starts the pump, thus evacuating space 38. When a predetermined degree of vacuum has been reached, a pressure-responsive switch closes, initiating the exposure operation by energizing the lamp and switching on the drive motor 34. The lamp carriage now traverses under glass sheet 31 from one side to the other to effect the exposure; the rate of traverse, and hence the exposure, can be controlled by a sliding tap on an autotransformer in the motor circuit. When the end of the traverse is reached, one of the limit switches is actuated, which de-energizes the lamp, and stops motor 34. At the same time, a solenoid valve 90 is energized which opens to release the vacuum in the frame 30, and also a vacuum brake 91 applies a brake shoe 101 to a friction disc 100 carried on the drive screw 71, thus preventing the carriage from over-running due to its momentum. When the vacuum has been released, the frame cover can be raised, thus opening the main cover switch. A cooling fan 25 with a separate motor 26 is provided. Fig. 14 (not shown) gives the details of the electrical circuit controlling the operation of the apparatus.